This invention relates to an improved electrode and electrolyte flow path for electrochemical machining.
Electrochemical machining is a known process in which an electrode is placed a predetermined gap distance from a workpiece, and an electrolyte is allowed to flow into the gap between the electrode and the workpiece. Current is passed between the electrode and the workpiece, and an electrochemical process occurs which removes material from the workpiece at positions opposed to the electrode.
In electrochemical machining apparatuses, it is of the utmost importance to ensure that the predetermined gap between the electrode and the workpiece is maintained at all times. If the gap is too small, it is possible to short-circuit the electrode and stop the removal of material from the workpiece. If the gap is too large, electrochemical action will cease and no metal will be removed.
It is also important to ensure that the electrolyte is uniformly distributed about the electrode throughout the area of the workpiece upon which the electrochemical machining is to be performed. If the concentration of electrolyte is not uniform cross the entire area to be machined, it is possible that the areas of greater electrolyte concentration will be more rapidly removed, and thus there may be uneven removal from the workpiece. This in turn can quickly cause the gap between the electrode and the workpiece to vary from the predetermined gap and may short-circuit the apparatus.
The problems with maintaining the gap between the electrode and the workpiece become particularly apparent when the workpiece is a curved or tubular member. Since the outer periphery of the workpiece will be extending along a curved radius in such a member, it is difficult to accurately position an electrode with respect to the workpiece. In the prior art, a hollow cylindrical electrode was utilized, and the electrolyte was passed through the center of the electrode. Such an electrode proved undesirable since the electrode in this arrangement would extend over too great a surface area, and due to the curvature of the workpiece, it was difficult to accurately maintain a desired gap between the electrode and the curved or tubular workpiece. If a cylindrical electrode is tilted there would not be an even gap between the electrode and the workpiece. This is true even for a flat surface workpiece.
In several electrochemical machining applications, the conventional method of supplying electrolyte to the gap between the electrode and the workpiece is inadequate. Electrochemical machining at an oblique angle into a flat surface or at any angle into a curved surface are examples of these applications. The electrolyte flows to the place of least resistance, normally the largest gap, and not through the tightest gap, thus resulting in an area of inadequate electrolyte allowing the electrode to contact the workpiece which may damage the workpiece or the electrode. These applications are not adequately performed with standard electrochemical machining methods since the electrolyte cannot be controlled, or at best additional external restraints are required to ensure that the electrolyte is properly supplied to the gap between an electrode and a workpiece.
Also, problems are encountered with standard electrochemical machining methods at the moment of breakthrough of a drilled hole or the like. Since a drilled hole tends to break through at a center point first, the electrolyte may often escape through the breakthrough hole before the entire drilled hole is machined to its full dimension. When this happens, there :s a possibility of the electrode again contacting the workpiece, increasing the likelihood of a short circuit.
It is known in electro-discharge machining to supply a dielectric machining fluid to the outer periphery of a cylindrical electrode as a coolant and to remove waste materials from the gap between the electrode and the workpiece. However, electrochemical machining is a much different process than electro-discharge machining and uses a different fluid.
It is therefore an object of the present invention to disclose an electrode holder and electrode shape to be utilized for electrochemical machining of tubular workpieces in which the electrode has a conical point, and an electrolyte is supplied in adequate amounts at the outer periphery and at the center of the electrode to ensure even removal of material from the workpiece. The electrolyte is supplied in adequate amounts even when the electrochemical machining is performed on workpieces of such shapes, or at such angles, as to make proper electrolyte flow difficult by conventional methods.